<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <title></title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .content{
            display: flex;
        }
        .sub{
            width: 200px;
            height: 500px;
            background:blue;
        }
        .main{
            flex:1;
            height: 500px;
            background:red;
        }
        .extra{
            width: 180px;
            height: 500px;
            background:green;
        }
    </style>
</head>
<body>
<!--  flex布局 -->
<div class="content">
    <div class="sub"></div>
    <div class="main"></div>
    <div class="extra"></div>
</div>
</body>
</html>